1. Field of the Invention
The present invention relates to a method for producing a lactam by oxidizing an alicyclic primary amine. More particularly, the present invention is concerned with a method for producing a lactam, which comprises subjecting an alicyclic primary amine to an oxidation reaction in the gaseous phase in the presence of molecular oxygen and a catalyst comprising a silicon oxide, to thereby obtain a lactam, and separating the lactam from a reaction system of the oxidation reaction. In addition, the present invention also relates to a catalyst comprising a silicon oxide, which is for use in the above-mentioned method. The method of the present invention not only prevents the by-production of ammonium sulfate which is of little commercial value, but also needs no cumbersome operations involved in conventional methods for producing a lactam, such as synthesis of hydroxylamine salt (which can be obtained only by a process involving complicated steps) and circulation of a buffer solution, and involves no step of producing an intermediate oxime, which should be followed by an oxime purification operation, and, hence, a lactam can be produced from an alicyclic primary amine very easily.
2. Prior Art
In the field of organic chemical industry, lactams are compounds useful as raw materials for polymers, pharmaceuticals, agricultural chemicals and the like. In the case of ε-caprolactam, this compound has been used for producing fibers and resins, and is especially useful as a raw material for nylon 6.
Various processes for producing lactams, such as ε-caprolactam, are conventionally known. As examples of such conventional processes, there can be mentioned the processes described in “Kougyou Yuuki Kagaku (Industrial Organic Chemistry)”, fourth edition, page 240 (1976), written by von Klaus Weissermel and Hans-Jurgen Arpe, translated under supervision of Teruaki Mukaiyama, TOKYO KAGAKU DOZIN CO., LTD., Japan (von Klaus Weissermel und Hans-Jurgen Arpe, “INDUSTRIELLE ORGANISCHE CHEMIE”, Verlag Chemie Gmbh (1976)), which processes include:
(A) cyclohexanone oxime process in which cyclohexanone oxime is synthesized directly or through an intermediate compound (cyclohexanone) from cyclohexane, and the synthesized cyclohexanone oxime is subjected to Beckman rearrangement, to thereby obtain ε-caprolactam;
(B) cyclohexanecarboxylic acid process in which toluene is oxidized in air to produce benzoic acid, the produced benzoic acid is hydrogenated to produce cyclohexanecarboxylic acid, and the produced cyclohexanecarboxylic acid is reacted with nitrosylsulfuric acid in the presence of fuming sulfuric acid, to thereby obtain ε-caprolactam;
(C) caprolactone process in which cyclohexanone is oxidized with peracetic acid to produce ε-caprolactone, and the produced ε-caprolactone is reacted with ammonia to thereby obtain ε-caprolactam; and
(D) nitrocyclohexanone process in which cyclohexanone is acetylated to obtain cyclohexenyl acetate, the obtained cyclohexenyl acetate is nitrated to obtain 2-nitrocyclohexanone, the obtained 2-nitrocyclohexanone is subjected to hydrolysis, thereby causing ring cleavage of the 2-nitrocyclohexanone to obtain nitrocapronic acid, the obtained nitrocapronic acid is hydrogenated to obtain ε-aminocapronic acid, and the obtained ε-aminocapronic acid is converted into ε-caprolactam.
Among the above-mentioned processes (A) to (D), the cyclohexanone oxime process (A) and the cyclohexane carboxylate process (B) have been practiced on a commercial scale. Especially, the cyclohexanone oxime process (A) has been practiced worldwide and is the most important.
The representative method for producing a lactam by the cyclohexanone oxime process is a method in which cyclohexanone oxime is produced from cyclohexanone and a hydroxylamine salt and, then, ε-caprolactam is synthesized from the produced cyclohexanone oxime by the Beckman rearrangement performed using sulfuric acid. The Raschig process, which is a classical oximation process, involves the steps of reducing ammonium nitrate using SO2 to obtain a disulfonate, and hydrolyzing the obtained disulfonate to obtain a hydroxylamine salt of sulfuric acid salt. The Raschig process practiced on a commercial scale involves four steps which are very complicated. Further, in this process, the amount of ammonium sulfate by-produced during the oximation performed using the above-mentioned hydroxylamine salt of sulfuric acid salt is approximately two moles per mole of the finally produced lactam. When the amount of ammonium sulfate by-produced in the Beckman rearrangement performed using sulfuric acid is also taken into consideration, the amount of ammonium sulfate by-produced in the Raschig process is approximately four moles per mole of the finally produced lactam. The commercial value of ammonium sulfate as a raw material for a fertilizer is no longer high, and the necessity of disposal of the by-produced ammonium sulfate is a great disadvantage of this process.
In this situation, for suppressing the by-production of ammonium sulfate, the hydroxylamine sulfate oxime process (HSO process) and the hydroxylamine phosphate oxime process (HPO process) have been proposed.
The HSO process (see, for example, U.S. Pat. Nos. 3,941,838 and 4,031,139) involves oxidizing ammonia in the presence of a platinum-containing catalyst to obtain NO, subjecting the obtained NO to reduction with hydrogen in the presence of a platinum-containing catalyst using an ammonium hydrogensulfate/ammonium sulfate buffer solution to produce hydroxylammonium sulfate, and reacting the produced hydroxylammonium sulfate with cyclohexanone.
The HPO process (see, for example, U.S. Pat. Nos. 3,948,988 and 3,940,442) involves oxidizing ammonia to obtain a nitric acid ion, subjecting the obtained nitric acid ion to reduction with hydrogen in the presence of palladium as a catalyst using a phosphoric acid/monoammonium phosphate buffer solution to produce a hydroxylamine salt of phosphoric acid, and reacting the produced hydroxylamine salt of phosphoric acid with cyclohexanone.
Each of the above-mentioned HSO and HPO processes is advantageous in that the buffer solution is allowed to circulate between the cyclohexanone oxime production system and the hydroxylamine salt production system, so that by-production of ammonium sulfate can be prevented. However, each of the processes has the following disadvantages. The process involves a number of reaction steps. Furthermore, the step of circulating the buffer solution is complicated.
As another improved process, there is known a process involving reacting cyclohexanone with ammonia and hydrogen peroxide in the presence of a solid catalyst to obtain cyclohexanone oxime (see U.S. Pat. No. 4,745,221). This method is advantageous not only in that the production of hydroxylamine salt is not needed and, hence, the circulation of the buffer solution is not needed, but also in that ammonium sulfate is not by-produced. However, in this method, although the oximation is not accompanied by the by-production of ammonium sulfate, ammonium sulfate is by-produced during the synthesis of a lactam as long as the Beckman rearrangement of an oxime for obtaining ε-caprolactam is performed using sulfuric acid.
Cyclohexanone oxime processes involving no step of producing intermediate cyclohexanone have also been practiced. As an example of such processes, there can be mentioned the photo-nitrosylation process which involves reacting cyclohexane with a gaseous mixture of hydrogen chloride and nitrosyl chloride by light irradiation using a mercury lamp to obtain an oxime. This method is advantageous in that ammonium sulfate is not by-produced. However, the method has the following disadvantages. Light is needed for the oximation, so that not only is a large amount of power needed for the oximation, but also maintenance of a mercury lamp or the like used for irradiation of light is cumbersome.
As another example of the cyclohexanone oxime processes involving no step of producing intermediate cyclohexanone, there can be mentioned a method which comprises subjecting cyclohexylamine to oxidation in the presence of a catalyst in the liquid or gaseous phase to thereby obtain cyclohexanone oxime. This method is advantageous in that ammonium sulfate is not by-produced.
However, although this method is not accompanied by the by-production of ammonium sulfate during the oximation step, ammonium sulfate is by-produced during the synthesis of a lactam as long as the Beckman rearrangement of an oxime for obtaining ε-caprolactam is performed using sulfuric acid.
In this situation, several attempts have been made to prevent the by-production of ammonium sulfate during the Beckman rearrangement. For example, a gaseousphase Beckman rearrangement reaction using a solid catalyst is known as a Beckman rearrangement reaction which is free from the by-production of ammonium sulfate. In most cases, the gaseous-phase Beckman rearrangement reaction is performed by a method in which an oxime is converted to ε-caprolactam in the gaseous phase in the presence of a zeolite type catalyst in a fixed-bed reactor or fluidized-bed reactor. In this method, ammonium sulfate is not by-produced because sulfuric acid is not used.
By combining the above-mentioned conventional processes, for example, by combining the oximation of cyclohexanone using hydrogen peroxide and the gaseousphase Beckman rearrangement of the resultant oxime, it is possible to obtain a method for producing a lactam, which is free from the by-production of ammonium sulfate and cumbersome operations, such as synthesis of hydroxylamine salts and circulation of a buffer solution, and which does not consume a large amount of electricity for providing light energy to the reaction system. However, the above-mentioned method comprising the conventional processes has the following disadvantages. In this method, the production of the intermediate oxime necessitates a purification process for oxime. In other words, the solvent used in the oximation process, unreacted ammonia and by-produced water must be separation-removed from the oximation reaction mixture before subjecting the produced oxime to the gaseous-phase Beckman rearrangement. In addition, the solid catalyst used for the gaseous-phase Beckman rearrangement reaction is likely to be poisoned by impurities by-produced in a trace amount and, therefore, a high degree purification of the oxime becomes necessary.
Thus, there has been no conventional method for producing a lactam, which is free from the by-production of ammonium sulfate and the necessity for cumbersome operations, such as synthesis of hydroxylamine salts and circulation of a buffer solution, and which needs no oxime purification operation (i.e., which involves no step of producing an intermediate oxime).